A case of immature complex odontoma was examined by light and electron microscopy, looking for additional information on odontogenic, tissue‐associated eosinophilic material (EM). Moreover, the ultrastructural morphology of the lesion was related to normal odontogenesis. Firstly, EM appeared to represent two different kinds of material, both being akin to predentin. Secondly, it is supposed that heterotypic epithelio‐mesenchymal cellular contacts have to be interpreted in terms of ultimateodontoblastic differentiation and have nothing to do with stimulation of the transformation of pre‐ameloblasts into enamel producing ameloblasts. In the third place, it is supposed that aberrant histogenetic differentiation in the odontomas is due to a failure of the mesenchymal component to respond normally to epithelial inductive influences.